The present invention relates to an optical disc signal recording method and an optical disc apparatus.
In an optical disc apparatus for recording data using an optical disc such as CD-R/RW, DVD+R/RW or DVD-RAM, a record pit or mark is formed by applying a laser beam generated from a semiconductor laser on a recording surface of an optical disc and focusing it to cause its thermal energy to change the physical property of the recording surface. The recording principle is based on a heat accumulation phenomenon. Thus, in order to form a record mark faithful to data to be recorded, the waveform of a laser beam to be applied is devised in various ways. That is, in the optical disc apparatus, various optimum waveforms of a laser pulse are finely set previously according to the length (mark length) of a recording signal or a recording speed, and the laser beam is applied onto the optical disc based thereon. The optimum waveform setting for the laser pulse will be referred to as “write strategy”, hereinafter.
In order to form a single record mark, there are employed, as typical write strategies, a system wherein the record mark is formed not using a single laser pulse but using a pulse train including a plurality of short pulses (multi-pulse type), and a system wherein two levels of amplitude of a recording pulse, that is, two levels of laser power are combined into a single composite pulse (called “castle type” because the waveform shape is similar to a castle shape) (refer to JP-A-2003-85753 and JP-A-2004-355809 as an example). With the above typical systems, a width increasing phenomenon caused in the last part of a record mark by heat accumulation can be avoided and a mark having a nearly uniform width can be formed. In a high-speed recording mode, since it is difficult to process a pulse train in the multi-pulse type, the castle type is advantageous thereover.
In the write strategies disclosed in JP-A-2003-85753 and JP-A-2004-355809, the castle type laser pulse is employed for a signal-having a long record mark; while a simple single pulse is employed for a signal having a short record mark. A single pulse is employed for a signal having a mark length of 4T (where T is a channel clock period) or shorter in JP-A-2003-85753, whereas, a single pulse is employed for a signal having a mark length of 3T in JP-A-2004-355809.
However, when the record pulse system is switched between the castle type and single pulse type according to the mark length, this also makes the setting of the write strategy complex. In particular, in such circumstances that, as a recording speed is increased, the recording system is shifted from the CLV (constant linear velocity) system to the CAV (constant angular velocity) system; a more complicated write strategy is required for the change in the recording speed and this requires an adjustment work time. This is expected that such a system will lead to difficulty in securing a good quality of recording.